Over the Air Testing for Massive MIMO Arrays

ABSTRACT

The disclosed system for testing a massive MIMO beamforming antenna array of arbitrary size includes an anechoic chamber, and a mount for a MIMO array antenna positioned in the chamber, wherein the array has at least 8×4 antenna elements that are individually activated to steer transmissions from the array. The system includes dual element antenna probes positionable in the anechoic chamber, with feeds coupling one or more UE sources to the antenna probes; and the UE sources generate RF in OTA communication with the array, emulating multiple UE devices. Additionally the system includes base station electronics coupled to the array, and a test controller coupled to the base station electronics. The test controller signals the UE sources OTA via the array to invoke a connection to the UE sources and measure OTA channel performance between the array and the multiple UE devices emulated, the performance including at least throughput.

RELATED APPLICATIONS

This application is a continuation of claims the benefit of U.S. patentapplication Ser. No. 15/620,610, entitled “OVER THE AIR TESTING FORMASSIVE MIMO ARRAYS”, filed on Jun. 12, 2017 (Attorney Docket No. SPIR1107-2), which claims the benefit of U.S. Provisional Application No.62/350,131, entitled “OVER THE AIR TESTING FOR MASSIVE MIMO ARRAYS,”filed on Jun. 14, 2016 (Attorney Docket No. SPIR 1107-1), which isincorporated by reference herein.

This application is related to U.S. patent application Ser. No.14/801,746, entitled “Massive MIMO Array Emulation,” filed Jul. 16, 2015(Attorney Docket No. SPIR 1100-1), which is incorporated by referenceherein.

This application is related to U.S. patent application Ser. No.13/147,579, entitled “Emulation and Controlled Testing of MIMO OTAChannels,” filed Aug. 29, 2011, now U.S. Pat. No. 8,995,511, issued Mar.31, 2015 (Attorney Docket No. SPIR 1018-6), which is incorporated byreference herein.

BACKGROUND

Massive multiple-input multiple-output (MIMO) provides an effectivemeans for significantly increasing the capacity of cellularcommunication systems while possibly reducing their energy consumption.Multiple-Input-Multiple-Output (MIMO) antenna techniques are key factorsin achieving the high data rates promised by next-generation wirelesstechnologies such as LTE (Long-Term Evolution), LTE-Advanced and planned5^(th) generation technologies.

MIMO systems are designed to take advantage of spatial diversityavailable in the propagation environment. The spatial diversity isquantified by the correlation between antennas, a function of both thepropagation environment and the antenna patterns. Under ideal conditionsan M×N MIMO system (one using M transmitting antenna elements and Nreceiving antenna elements) can increase maximum data rates by a factorof min{M,N}times those available from a Single-Input Single-Output(SISO) system operating in the same bandwidth. In other words, a 4×2MIMO system can (under ideal conditions) double the data rates availablein a SISO implementation, while a 4×4 MIMO system can potentiallyquadruple those rates. However, classical array modeling via MIMOemulation is expensive and prohibitively complex to build, and channelemulators have a limited number of possible inputs.

As the demand for higher bandwidths continues to grow, designers usehigher frequencies—for example, as high as 60 gigahertz. When higherfrequencies are used, the size of transmit antenna elements decreases,with a result that each element produces lower path gains—with aresulting power change of as much as 30 dB less. The use of massive MIMOboosts resulting beam signal strength. There is also a demand formultiple users in the same cell with separate signals, calledmultiple-user MIMO.

Emulation of massive MIMOs makes it possible to group hundreds of fadinglinks computed in hardware into a tractable number of virtual elements,for increasing data rates and for testing for massive MIMOs.

An opportunity arises to provide systems and methods for testing massiveMIMO arrays.

SUMMARY

One implementation of the disclosed technology teaches a system thattests a massive MIMO array antenna. The system includes an anechoicchamber, and a mount for a MIMO array antenna positioned in the chamber,wherein the array has at least 8×4 antenna elements that areindividually activated to steer transmissions from the array. The systemalso includes at least four dual element antenna probes positionable inthe anechoic chamber, with feeds coupling one or more UE sources to theantenna probes; and the UE sources generate RF in over-the-aircommunication with the array, emulating multiple UE devices.Additionally the system includes base station electronics coupled to thearray, and a test controller coupled to the base station electronics,wherein the test controller signals the UE sources over-the-air via thearray to invoke a connection to the UE sources and measure over-the-airchannel performance between the array and each of the multiple UEdevices emulated, the performance including at least throughput.

Particular aspects of the technology disclosed are described in theclaims, specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 shows an example massive MIMO array environment.

FIG. 2 shows a massive MIMO array antenna in an anechoic chamber.

FIG. 3 illustrates, for a multi-user LOS and NLOS test, a top view,perspective view and an azimuth and elevation map that plots positionsof UEs across the field of view.

FIG. 4 illustrates spatial correlation results, for two probes, at an MMarray.

FIG. 5 shows a multi-user LOS and NLOS test map for comparing isolationbetween beams.

FIG. 6 illustrates an adaptive probe layout map for multi-user LOS andNLOS tests.

FIG. 7 illustrates another adaptive probe layout map for multi-user LOSand NLOS tests, in which the probe locations are chosen to create a setof similar path directions.

FIG. 8 illustrates the channel matrix inside the channel emulatorreferenced to the downlink.

FIG. 9 displays probes observed from the center of test volume, withunrelated streams from different parts of the array.

FIG. 10 is a simplified block diagram of a system for emulating amassive MIMO array.

FIG. 11 illustrates spatial correlation results, for three probes, at anMM array.

DETAILED DESCRIPTION

The following description of the disclosure will typically be withreference to specific embodiments and methods. It is to be understoodthat there is no intention to limit the disclosure to the specificallydisclosed embodiments and methods, but that the disclosure may bepracticed using other features, elements, methods and embodiments.Preferred embodiments are described to illustrate the presentdisclosure, not to limit its scope. Those of ordinary skill in the artwill recognize a variety of equivalent variations on the descriptionthat follows. Like elements in various embodiments are commonly referredto with like reference numerals.

Massive MIMO systems are generally designed to communicate with one tomany simultaneous users. FIG. 1 illustrates a possible OTA MIMO arraytesting environment, which contains a massive MIMO array of antennas(MM) 112, and a mix of line-of-sight (LOS) 114, 162 andnon-line-of-sight (NLOS) 162, 168 users scattered about a coverage area.For NLOS users, the propagation paths are obstructed in someway—creating a set of sub-components of the path, which are modeled byan angle spread (AS). The AS observed at the base station is usuallyquite narrow, being a few degrees in azimuth and elevation. The spreadin azimuth is usually a bit more than the spread in elevation. The ASobserved by the user equipment (UE) 168 is generally much higher due tothe proximity to the scattering elements 116, 166. Sometimes a commonscattering element may provide signal to more than one UE.

Massive MIMO array antennas may have a large number of radiatingelements, usually in a rectangular grid 112 with element spacing equalto one half the wavelength of the carrier frequency. This spacing mayvary, but is usually less than the wavelength of the carrier frequency.When dual polarized elements are used, often +/−45 degree antennaelements or 0/+90 degree elements are co-located, and spaced apart fromthe next pair of elements in the grid. These dual polarized elementsenable the antenna to couple signals to and from the channel in verticaland horizontal polarization. Massive MIMO array antennas are valid forboth uplink and downlink signals, supporting division duplexing (TDD) orfrequency division duplexing (FDD). Packets can be interspersed betweendownlink packets and uplink packets.

Multipath propagation is often observed for NLOS users. This type ofpropagation is indicated by having more than one path that reaches theUE, usually with each path having different path delays and differentangles of departure and arrival observed at the base station (BS) andthe UE respectively.

The disclosed technology emulates a mixed environment, having one ormore users, which will experience one of several different propagationmechanisms, e.g. some as described above, in order to test a massiveMIMO system.

FIG. 2 shows a massive MIMO array antenna 214 with narrow angle spreadand high correlation, in an anechoic chamber 212 and connected to amount 244 that can be controlled for tilting and rotating the array,which is needed when a test requires the array to be repositioned. Inone implementation, mount 244 can be a two axis positioner stand. Arotation-only mount can be used in some cases, as it can be dramaticallyless expensive than a mount that includes tilt. In other test cases twodegrees of freedom, including both rotation and tilt, or three degreesof freedom including rotation, tilt and roll are needed for testing of aMIMO array antenna positioned in the chamber. Several probe antennaelements 216, 246 are shown on the right side of the chamber, eachhaving a vertical and a horizontal element configured as a “+” with eachelement being connected to an RF cable 218, 248 that leads outside thechamber to a Spirent Vertex Channel Emulator 219. The Spirent VertexChannel Emulator platform supports scalable emulation to support a rangeof applications that require varying channel densities, from basicapplications like two-channel SISO to complex, high channel densityapplications like MIMO OTA and carrier aggregation, and supportsconfigurations to evaluate future technologies such as 5G.

In some cases amplifier stages may be utilized between one or more probeelements and the channel emulator to condition the signal level. Asplitter may also be used to drive more than one input of the channelemulator from a single probe antenna element in order to emulate some ofthe channel conditions of interest, or to facilitate the case of usingmultiple carrier frequencies. The operation of the massive MIMO arrayantenna 214 is typically bi-directional, so both uplink and downlinksignals are emulated. It is usually a time division duplex (TDD) systemwith the same carrier frequency used on the uplink and downlink, but itmay also be a frequency division duplex (FDD) system, with differentfrequencies used on the uplink and downlink. UE 266, 267 and 268 can bephones or emulated phones. A BS or BS emulator controls the UE, settingup a test mode, creating or simulating data, measuring throughput (TP),and monitoring both the uplink and downlink.

The LOS path 245 is emulated by a single dual polarized probe 255, sothat the MIMO array antenna 214 sees only a single angle in azimuth andelevation to this probe. Thus there is no AS observed at the MIMO arrayantenna 214 and a static channel is assumed for the emulated propagationpath within the channel emulator. For the NLOS path 215, two dualpolarized probe antennas 216 are utilized to facilitate a specificazimuth and elevation spread. Referenced to the downlink, this would bean azimuth spread of departure (ASD) and elevation spread of departure(ESD). Although two dual polarized probes 216 are shown, three or moremay be needed in order to meet the target characteristics of the ASD andESD across the MM array dimensions.

FIG. 3 illustrates, for a multi-user LOS and NLOS test, a top view 312of the possible probe placement in the anechoic chamber, and aperspective view of a MM array 363 relative to a mix of probes 364, with3-axis positioner 362. Additionally an azimuth and elevation map 314plots positions of probes across the field of view, with the X axis asazimuth and the Y axis as elevation. The map 314 identifies severalprobe locations as possible positions in the chamber relative to thetest volume where the MM array 363 will be positioned. The map 314includes a callout for the measurement for azimuth spread 316 andelevation spread 318 for one NLOS probe set 326. Each dual polarized “+”probe shown on the map 314 represents a LOS path departure 366, 367,368, 369 for the downlink, and arrival for the uplink. Each dualpolarized pair of “+” antennas 326, 327, 328 and 329 represents a NLOSpath, which has a specific ASD and ESD for the downlink and acorresponding ASA and ESA for the uplink.

In terms of the downlink, the probe antennas illustrated in FIG. 3represent path departure angles to a set of UEs, similar to those shownin FIG. 1, in which each UE observes only a single path. In the case inwhich a user experiences multi-path, more than one departure angle mayarrive at the UE, and this would require an additional set of NLOSprobes. A single departure angle can provide signals to two UEs, as isalso illustrated in FIG. 1. In this case, the signals are split by an RFsplitter and fed to different inputs or outputs of the channel emulator,or may be routed to multiple UEs from within the channel emulator.

The probe positions shown in FIG. 3 are primarily spread out in azimuthmore than elevation, but the example MIMO array 363 has more elevationdiscrimination than azimuth because it has 16 dual polarized elements inthe vertical dimension and only 8 dual polarized elements in thehorizontal dimension. As one aspect of the test, the MIMO array 363 maybe rolled by 90 degrees, so that the 16 elements may be used to view theazimuth. If the probe arrangements are not symmetric with respect to thearray, it may also be useful to roll the array by 180 degrees so thatdifferent portions of the array can observer the chamber probes.

The position of the MIMO array 363 may also be tilted in elevation viathe 3 axis positioner 362 so that the probes in the anechoic chamber areobserved at a shifted elevation. Likewise, the MIMO array 363 may betilted in azimuth so that the probes in the chamber are observed at ashifted azimuth—a feature usable to test the performance for angles nearthe edges of the array.

FIG. 4 illustrates spatial correlation results at the MIMO array 363,showing the differences in elevation spread (ESD) and azimuth spread(ASD) 412 that may be observed as described by the “Winner+” model(reference: Winner+ D5.3_v1.0.pdf). Based on this reference amongothers, target values were chosen as ASD=5 degrees and ESD=2 degrees.With two probes having equal power and separated by an angle of Ndegrees, the RMS angle spread will be N/2 degrees.

Several models, including “SCME” and the “Winner” model utilize apredefined set of 20 sub-path components that are distributed to achievethe target AS. The SCME Cluster Model correlation plot 416 shows resultsfor AS values of 2, 2.5, 3, 4, and 5 degrees. Since the target valueschosen for this design are 2 degrees for ESD and 5 degrees for ASD,these two curves need to be observed across the horizontal and verticalarray dimensions. The array dimension is given with respect to a firstarray element at zero; that is, with the first element at zero, and theelements spaced by 0.5 lambda, the 8th element will be seen at 3.5lambda—where lambda is the wavelength of the carrier frequency. In thisexample, a 128 element array is considered, wherein the array has 16dual polarized “X” antennas in the vertical dimension and 8 dualpolarized “X” antennas in the horizontal. Thus we need to match thedesired curves to the 3.5 lambda point for the ASD 466 and the 7.5lambda point for the ESD 468. Two probes can align with the plottedspatial correlation curves for these parameters for the specified arraydimensions, wherein the alignment is not critical below about 0.3-0.4correlation 465, which is the point at which the channel looks like anuncorrelated receiver. For the two probe case, the AS isn't quite thesame as the AS of the target curves when the best alignment is achieved.This is because the AS calculated with two components compared to 20components is not quite a linear relationship. Thus the ESD (downlink)and ESA (uplink) values are a fraction of a degree less for the twoprobe design, which is expected. With two probes, the first “+” probe462 is given a different azimuth and elevation to that of the second “+”probe 464. This achieves both an ASD and ESD when observed in thechamber.

In the test case in which a larger array was used, such as a 256 elementarray, in which the width is doubled, then the match to the ASD must bemaintained out to 7.5 lambda and this is not possible with only twoprobes, because the correlation coefficient magnitude has a fly-backbehavior. In this case, three or more probes would be necessary and thepowers and angles of the probes would be optimized to achieve the ASDalignment over the full dimension of the array. It is possible toutilize two probes for ESD and three or more for ASD. However if theprobes are available, then utilizing them will improve the performanceof both ESD and ASD alignment. FIG. 11 shows a SCME Cluster Modelcorrelation plot 1122 that includes three probes 1112, 1114, 1116 withprobe power distribution of 0.33, 0.34 and 0.33, for ESD=1.8 1168 andfor ASD=4.5 1166. The behavior of the 3 probe example is shown to matchthe target ESD of 2 degrees and ASD of 5 degrees of the standardized 20sinusoid cluster channel model. The benefit of having 3 probes in thisexample is to maintain a match to the expected ASD characteristicfurther out in separation distance given by the Array Dimension inlambda. When the correlation is below a value of 0.3 to 0.4 the signalsbeing compared are considered uncorrelated, and an exact match is norequired as long as it stays below this level. As seen in the 3-probecurve 1166, the correlation matches well at the higher levels, i.e.above 0.4, and it maintains its low performance below 0.3-0.4 withoutthe fly-back behavior that resulted from 2 probes shown by 466. Thus the3 probe case can operate with a larger array size.

With the three probe case, the connection matrices shown in 812 and 912would include additional probe connections at 813, 815, and 915,corresponding to the larger probe count.

Note that although examples of 2 and 3 probes are shown as an approachto minimize the number of probes, it is possible to use a larger numberof probes, including a linear or two dimensional array of probes torepresent each cluster in the chamber, e.g. 327, 328, 329.

FIG. 5 shows a multi-user LOS and NLOS test map 512 for comparingisolation between beams. If users do not achieve maximum throughput,this test may indicate that beam overlap is degrading the signal tointerference (SIR) per user. When the probes are spatially distributedby some amount, the MIMO array system is designed to be able todistinguish the different propagation paths, which are connected todifferent users. Depending on the MIMO array, there may be somedegradation from incompletely isolating the users, and this would resultin limited SIR, and lead to reduced throughput (TP) to a user. This canbe tested by as shown in FIG. 5, by increasing the spacing between probeone 513 and probe six 514, between probe six 514 and probe three 516,and between probe three 516 and probe eight 564 to 45 degrees. In thiscase this effect is achieved by turning off some users, represented withdimmed “+” 515, 517, 561 and 563. The test compares TP per user with afully populated environment and TP per user with a sparsely populatedenvironment.

FIG. 6 illustrates an adaptive probe layout map 612 for multi-user LOSand NLOS tests, to show the concept of switching probe positions byeither physically moving the cable from one probe to another, or byutilizing an RF switch. In one example implementation, disconnecting orswitching off an antenna may include connecting a fifty ohm terminatorto reduce reflections from the unused probed. This provides a way toeffectively change the probe location in the chamber to modify the test.For one example test, the top row of probes is electrically switched toa higher row of probes 613, 615, 617 and 619 at +67.5 degrees. In sometest cases, the array can be tilted up, so that the simultaneous probeswill be positioned at +/−45 degrees.

FIG. 7 illustrates another adaptive probe layout map 712 for multi-userLOS and NLOS tests. In this example, the probe locations are chosen tocreate a set of similar path directions. This represents the case inwhich multiple users may be close together, and experience similarpropagation paths. For example, probe six 762, probe nine 761, and probeeleven 764 for NLOS users, and probe ten 716 and probe twelve 718 forLOS users. This is a difficult case for the MIMO array to resolve sincethese angles are close together and the array may not be able to do so,leading to reduction in TP to these users. This is an important testcase in which there is spatial coherence between users.

FIG. 8 illustrates the channel matrix 812 inside the channel emulator,referenced to the downlink. The chamber probes 813, 815 and 862 areshown on the left, and are connected to the inputs of the channelemulator. The UE ports 814, 864 and 818 are shown on the right. Eachlink between the input and output represents a fading connection betweenthe base station (BS) and UE. For the NLOS case, the vertical andhorizontal probe elements that make up each path are uncorrelated suchthat the correlation between BS elements is set by the angle differencesbetween the probes, as described relative to FIG. 4. Correlations at theUE antenna elements are determined by the channel model and UE antennaassumptions. For the three probe case that supports wider arrays, alarger H matrix would be implemented.

FIG. 9 displays probes observed from the center of test volume912—showing unrelated streams 914 from different parts of MIMO array913. FIG. 9 further illustrates the 4×4 MIMO channel emulation 916, inwhich the elevation spread for NLOS 915 and the azimuth spread for NLOS964 create the potential for decorrelation across the array, leading tofour separate streams being possible. FIG. 9 also includes 2×2 LOS MIMOchannel emulation 966.

Computer System

FIG. 10 is a simplified block diagram of an embodiment of a system 1000that can be used for testing a beamforming antenna array. MIMO arraytesting can be implemented using a computer program stored in systemmemory, or stored on other memory and distributed as an article ofmanufacture, separately from the computer system.

Computer system 1010 typically includes a processor subsystem 1072 whichcommunicates with a number of peripheral devices via bus subsystem 1050.These peripheral devices may include a storage subsystem 1026,comprising a memory subsystem 1022 and a file storage subsystem 1036,user interface input devices 1038, user interface output devices 1078,and a network interface subsystem 1076. The input and output devicesallow user interaction with computer system 1010 and network and channelemulators. Network interface subsystem 1074 provides an interface tooutside networks and devices of the system 1000. The computer systemfurther includes communication network 1084 that can be used tocommunicate with user equipment (UE) units; for example, as a deviceunder test.

The physical hardware component of network interfaces are sometimesreferred to as network interface cards (NICs), although they need not bein the form of cards: for instance they could be in the form ofintegrated circuits (ICs) and connectors fitted directly onto amotherboard, or in the form of microcells fabricated on a singleintegrated circuit chip with other components of the computer system.

User interface input devices 1038 may include a keyboard, pointingdevices such as a mouse, trackball, touchpad, or graphics tablet, ascanner, a touch screen incorporated into the display, audio inputdevices such as voice recognition systems, microphones, and other typesof input devices. In general, use of the term “input device” is intendedto include all possible types of devices and ways to input informationinto computer system 1010.

User interface output devices 1078 may include a display subsystem, aprinter, a fax machine, or non-visual displays such as audio outputdevices. The display subsystem may include a cathode ray tube (CRT), aflat panel device such as a liquid crystal display (LCD) or LED device,a projection device, or some other mechanism for creating a visibleimage. The display subsystem may also provide non visual display such asvia audio output devices. In general, use of the term “output device” isintended to include all possible types of devices and ways to outputinformation from computer system 1010 to the user or to another machineor computer system. The computer system further can include userinterface output devices 1078 for communication with user equipment.

Storage subsystem 1026 stores the basic programming and data constructsthat provide the functionality of certain embodiments of the presentinvention. For example, the various modules implementing thefunctionality of certain embodiments of the invention may be stored in astorage subsystem 1026. These software modules are generally executed byprocessor subsystem 1072.

Storage subsystem 1026 typically includes a number of memories includinga main random access memory (RAM) 1034 for storage of instructions anddata during program execution and a read only memory (ROM) 1032 in whichfixed instructions are stored. File storage subsystem 1036 providespersistent storage for program and data files, and may include a harddisk drive, a floppy disk drive along with associated removable media, aCD ROM drive, an optical drive, or removable media cartridges. Thedatabases and modules implementing the functionality of certainembodiments of the invention may have been provided on a computerreadable medium such as one or more CD-ROMs, and may be stored by filestorage subsystem 1036. The host memory storage subsystem 1026 contains,among other things, computer instructions which, when executed by theprocessor subsystem 1072, cause the computer system to operate orperform functions as described herein. As used herein, processes andsoftware that are said to run in or on “the host” or “the computer”,execute on the processor subsystem 1072 in response to computerinstructions and data in the host memory storage subsystem 1026including any other local or remote storage for such instructions anddata.

Bus subsystem 1050 provides a mechanism for letting the variouscomponents and subsystems of computer system 1010 communicate with eachother as intended. Although bus subsystem 1050 is shown schematically asa single bus, alternative embodiments of the bus subsystem may usemultiple busses.

Computer system 1010 itself can be of varying types including a personalcomputer, a portable computer, a workstation, a computer terminal, anetwork computer, a television, a mainframe, or any other dataprocessing system or user device. Due to the ever changing nature ofcomputers and networks, the description of computer system 1010 depictedin FIG. 10 is intended only as a specific example for purposes ofillustrating embodiments of the present invention. Many otherconfigurations of computer system 1010 are possible having more or lesscomponents than the computer system depicted in FIG. 10.

Some Particular Implementations

In one implementation, the disclosed technology includes a system thattests a massive MIMO array antenna, the system including an anechoicchamber; a mount for a MIMO array antenna positioned in the chamber,wherein the array has at least 8×4 antenna elements that areindividually activated to steer transmissions from the array; at least 3dual element antenna probes positionable in the anechoic chamber; feedscoupling one or more UE sources to the antenna probes, the UE sourcesgenerating RF in over-the-air communication with the array, the UEsources emulating multiple UE devices; base station electronics coupledto the array; and a test controller coupled to the base stationelectronics; wherein the test controller signals the UE sourcesover-the-air via the array to invoke a connection to the UE sources andmeasure over-the-air channel performance between the array and each ofthe multiple UE devices emulated, the performance including at leastthroughput. The UE sources are usable in both uplink and downlink tests.In some implementations, one probe can be associated with one UE and inthat case three UEs would be needed for the three probe system. In otherimplementations one UE is needed for the two probe NLOS case, and whenthe beam is spread, so that two probes emulate the angular spread, andone UE is needed for the one probe LOS case.

This system and other implementations of the technology disclosed caninclude one or more of the following features and/or features describedin connection with additional systems disclosed. In the interest ofconciseness, the combinations of features disclosed in this applicationare not individually enumerated and are not repeated with each base setof features. The reader will understand how features identified in thissection can readily be combined with sets of base features identified asimplementations.

In one implementation the disclosed system includes a mount controllableto rotate relative to a horizontal base of the anechoic chamber. Inother implementations, the mount is further controllable to tilt thearray relative to a point of attachment of the array to the mount. Inyet other implementations, the mount is further controllable to rollrelative to the point of attachment of the array to the mount.

In some implementations, the system further includes at least one pairof dual element antenna probes coupled to a single source, therebyemulating an angular spread in arrival direction among signal componentsof a signal originating at UE. The system can also include the feedscoupling one or more UE sources through a channel emulator that variesthe over-the-air channel conditions between the antenna probes and thearray.

One implementation of the disclosed system further includes the basestation electronics configured to send the UE sources commands over RFsignals to adjust UE power level, data connection and data rate. In someimplementations the system can further include a network emulatorcoupled between the test controller and the base station electronics,wherein the network emulator causes the base station electronics to sendsignals to the UE that control UE power level, data connection and datarate. Data connection can include the configuration details of the datatransmission, including details on the selection in LTE of the duplexmode, transmission mode, bandwidth, fixed reference channel, modulation,transmission block size, MIMO order, number of resource blocks or otherdetails about the data connection.

In some implementations, the UE sources include individual UE devices inindividual RF isolation boxes. In other implementations, the UE sourcesinclude a UE source device simulator that emulates the multiple UEdevices.

One implementation of the disclosed system includes a radio distributionunit, connected between the array and the base station electronics,wherein the radio distribution unit distributes signals to each arrayelement and controls one or more beam patterns by selectively weightingsignals distributed to the antenna elements by complex gain and delayvalues. The delay values can have a value of zero; with widerbandwidths, the delays may need to be compensated so that the phaseremains accurate across frequency. The disclosed system can furtherinclude a channel from the test controller to the channel emulator usedby the test controller to vary the over-the-air channel conditions. Inother implementations of the disclosed system, the channel from the testcontroller to the channel emulator is wired.

In some implementations of the disclosed system, the measuredover-the-air channel observed by the massive MIMO array is an emulationof a downlink channel. In other implementations, the measuredover-the-air channel observed by the massive MIMO array is an emulationof an uplink channel. In yet other implementations, the measuredover-the-air channel observed by the massive MIMO array is an emulationof a bi-directional channel, including downlink and uplink.

One implementation of the disclosed technology further includes a firstdistribution of test probes in the chamber that are substantiallyseparated to allow the massive MIMO to observe isolation betweendirections to multiple users, then evaluating the performance for thisset of probes according to a reference direction of the massive MIMOarray, wherein the massive MIMO array can be rotated or tilted or rolledto observe the performance when probes fall at the center versus at anedge of array coverage.

Another implementation of the disclosed technology further includes asecond distribution of test probes in the chamber that are substantiallyclumped in a similar area to allow the massive MIMO to observe lowerisolation between directions to multiple users, then evaluating theperformance for this set of probes according to a reference direction ofthe massive MIMO array, wherein the massive MIMO array can be rotated ortilted or rolled to observe the performance when probes fall at thecenter versus at an edge of array coverage.

Other implementations may include a method according to any of thepreceding systems, described above, including methods for testing amassive MIMO array antenna.

Yet other implementations include tangible non-transitory computerreadable storage media storing instructions executable by a processor tocontrol a system as described above. A tangible non-transitory computerreadable media does not include a transitory wave form.

We claim as follows:
 1. A system that tests a massive MIMO arrayantenna, the system including: an anechoic chamber; a mount for a MIMOarray antenna positioned in the anechoic chamber, wherein the MIMO arrayantenna has at least 8×4 antenna elements that are individuallyactivated to steer transmissions from the MIMO array antenna; at leastone pair of dual element antenna probes positionable in the anechoicchamber; feeds coupling one or more UE sources to the dual elementantenna probes, the UE sources generating RF in over-the-aircommunication with the MIMO array antenna, the UE sources emulatingmultiple UE devices; base station electronics coupled to the MIMO arrayantenna; a test controller coupled to the base station electronics;wherein the test controller signals the UE sources over-the-air via theMIMO array antenna to invoke a connection to the UE sources and measureover-the-air channel performance between the MIMO array antenna and eachof the multiple UE devices emulated, the performance including at leastthroughput; and a first distribution of test probes in the anechoicchamber, wherein dual element antenna probes in the first distributionof test probes are substantially clumped in an area to allow the MIMOarray antenna to observe isolation between directions to multiple users,then evaluating performance for the first distribution of test probesaccording to a reference direction of the MIMO array antenna, whereinthe MIMO array antenna can be rotated or tilted or rolled to observe theperformance when test probes fall at the center versus at an edge ofarray coverage.
 2. The system of claim 1, further including a single oneof the at least a plurality of dual element antenna probes coupled to asingle UE source.
 3. The system of claim 1, further including at least afirst UE source and a second UE source, a first set of 2 or more probescoupled to the first UE source and a second set of 2 or more probescoupled to the second UE source and wherein the first set of 2 or moreprobes and the second set of 2 or more probes share at least one probe.4. The system of claim 1, wherein elements of at least one dual elementantenna probe are substantially orthogonal, and further includingapplying a first signal from a first UE to a first element of the atleast one dual element antenna probe and a second signal from a secondUE to a second element of the at least one dual element antenna probe.5. The system of claim 1, further including increasing spacing betweenselected test probes in the anechoic chamber wherein dual elementantenna probes of selected test probes are spatially distributed toallow the MIMO array antenna to observe a change in isolation betweendirections to multiple users, then evaluating performance for this setof test probes according to a reference direction of the MIMO arrayantenna, wherein the MIMO array antenna can be rotated or tilted orrolled to observe performance when test probes fall at the center versusat an edge of array coverage.
 6. The system of claim 1, furtherincluding a second distribution of a set of test probes in the anechoicchamber wherein dual element antenna probes in the set of test probesare substantially separated to allow the MIMO array antenna to observe achange in isolation between directions to multiple users, thenevaluating performance for this set of test probes according to areference direction of the MIMO array antenna, wherein the MIMO arrayantenna can be rotated or tilted or rolled to observe performance whentest probes fall at the center versus at an edge of array coverage.
 7. Amethod for testing a MIMO array antenna, the method including:positioning a MIMO array antenna on a mount in an anechoic chamber,wherein the MIMO array antenna has at least 8×4 antenna elements thatare individually activated to steer transmissions from the MIMO arrayantenna; using at least one pair of dual element antenna probespositioned in the anechoic chamber, generating RF in over-the-aircommunication with the MIMO array antenna, with feeds coupling one ormore UE sources to the dual element antenna probes, wherein the UEsources emulate multiple UE devices; signaling the UE sourcesover-the-air via the MIMO array antenna, using base station electronicscoupled to a test controller, connecting with the UE sources; evaluatingperformance according to a reference direction of the MIMO array antennafor a first distribution of test probes in the anechoic chamber whereindual element antenna probes in the first distribution of test probes aresubstantially clumped in an area to allow the MIMO array antenna toobserve isolation between directions to multiple users, wherein the MIMOarray antenna can be rotated or tilted or rolled to observe theperformance when probes fall at the center versus at an edge of arraycoverage; and measuring over-the-air channel performance between theMIMO array antenna and each of the multiple UE devices emulated, theperformance including at least throughput.
 8. The method of claim 7,wherein a single one of the at least a plurality of dual element antennaprobes coupled to a single UE source.
 9. The method of claim 7, furtherincluding at least a first UE source and a second UE source, a first setof 2 or more probes coupled to the first UE source and a second set of 2or more probes coupled to the second UE source, and wherein the firstset of 2 or more probes and the second set of 2 or more probes share atleast one probe.
 10. The method of claim 7, wherein elements of at leastone dual element antenna probe are substantially orthogonal, and furtherincluding applying a first signal from a first UE to a first element ofthe at least one dual element antenna probe and a second signal from asecond UE to a second element of the at least one dual element antennaprobe.
 11. The method of claim 7, further including: increasing spacingbetween selected test probes within the anechoic chamber, wherein dualelement antenna probes of selected test probes are spatially distributedto allow the MIMO array antenna to observe a change in isolation betweendirections to multiple users; evaluating performance according to thereference direction of the MIMO array antenna for the test probes,wherein the MIMO array antenna can be rotated or tilted or rolled toobserve performance when test probes fall at the center versus at anedge of array coverage.
 12. The method of claim 7, further including:evaluating performance according to the reference direction of the MIMOarray antenna for a second distribution of test probes in the anechoicchamber wherein dual element antenna probes in the second distributionof test probes are substantially separated to allow the MIMO arrayantenna to observe a change in isolation between directions to multipleusers, wherein the MIMO array antenna can be rotated or tilted or rolledto observe performance when test probes fall at the center versus at anedge of array coverage.
 13. A tangible non-transitory computer readablemedia with instructions that are combinable with a processor and memorycoupled to the processor to carry out a method for testing a massiveMIMO array antenna positioned within an anechoic chamber and havingindividually activated antenna elements to steer transmissions from thearray, the method including: using at least one pair of dual elementantenna probes positioned in the anechoic chamber, generating RF inover-the-air communication with the MIMO array antenna, with feedscoupling one or more UE sources to the dual element antenna probes,wherein the UE sources emulate multiple UE devices; signalingover-the-air via the MIMO array antenna, the UE sources using basestation electronics coupled to a test controller, connecting with the UEsources; evaluating performance according to a reference direction ofthe MIMO array antenna for a first distribution of test probes in theanechoic chamber wherein dual element antenna probes in the firstdistribution of test probes are substantially clumped in an area toallow the MIMO array antenna to observe isolation between directions tomultiple users, wherein the MIMO array antenna can be rotated or tiltedor rolled to observe the performance when probes fall at the centerversus at an edge of array coverage; and measuring over-the-air channelperformance between the MIMO array antenna and each of the multiple UEdevices emulated, the performance including at least throughput.
 14. Thetangible non-transitory computer readable media of claim 13, wherein asingle one of the at least a plurality of dual element antenna probescoupled to a single UE source.
 15. The tangible non-transitory computerreadable media of claim 13, further including at least a first UE sourceand a second UE source, a first set of 2 or more probes coupled to thefirst UE source and a second set of 2 or more probes coupled to thesecond UE source, and wherein the first set of 2 or more probes and thesecond set of 2 or more probes share at least one probe.
 16. Thetangible non-transitory computer readable media of claim 13, whereinelements of at least one dual element antenna probe are substantiallyorthogonal, and further including applying a first signal from a firstUE to a first element of the at least one dual element antenna probe anda second signal from a second UE to a second element of the at least onedual element antenna probe.
 17. The tangible non-transitory computerreadable media of claim 13, further including: increasing spacingbetween selected test probes within the anechoic chamber, wherein dualelement antenna probes of selected test probes are spatially distributedto allow the MIMO array antenna to observe a change in isolation betweendirections to multiple users; and evaluating performance according tothe reference direction of the MIMO array antenna for the test probes,wherein the MIMO array antenna can be rotated or tilted or rolled toobserve performance when test probes fall at the center versus at anedge of array coverage.
 18. The tangible non-transitory computerreadable media of claim 13, further including: evaluating performanceaccording to the reference direction of the MIMO array antenna for asecond distribution of test probes in the anechoic chamber wherein dualelement antenna probes in the second distribution of test probes aresubstantially separated to allow the MIMO array antenna to observe achange in isolation between directions to multiple users, wherein theMIMO array antenna can be rotated or tilted or rolled to observeperformance when test probes fall at the center versus at an edge ofarray coverage.